1. Field of the Invention
The invention relates generally to occlusion devices for closing physical anomalies, such as an atrial septal defect, a patent foramen ovale, and other septal and vascular defects.
2. Description of Related Art
A patent foramen ovale (PFO), illustrated in FIG. 1, is a persistent, one-way, usually flap-like opening in the wall between the right atrium 11 and left atrium 13 of the heart 10. Because left atrial (LA) pressure is normally higher than right atrial (RA) pressure, the flap usually stays closed. Under certain conditions, however, right atrial pressure can exceed left atrial pressure, creating the possibility that blood could pass from the right atrium 11 to the left atrium 13 and blood clots could enter the systemic circulation. It is desirable that this circumstance be eliminated.
The foramen ovale serves a desired purpose when a fetus is gestating in utero. Because blood is oxygenated through the umbilical chord, and not through the developing lungs, the circulatory system of the fetal heart allows the blood to flow through the foramen ovale as a physiologic conduit for right-to-left shunting. After birth, with the establishment of pulmonary circulation, the increased left atrial blood flow and pressure results in functional closure of the foramen ovale. This functional closure is subsequently followed by anatomical closure of the two over-lapping layers of tissue: septum primum 14 and septum secundum 16. However, a PFO has been shown to persist in a number of adults.
The presence of a PFO is generally considered to have no therapeutic consequence in otherwise healthy adults. Paradoxical embolism via a PFO is considered in the diagnosis for patients who have suffered a stroke or transient ischemic attack (TIA) in the presence of a PFO and without another identified cause of ischemic stroke. While there is currently no definitive proof of a cause-effect relationship, many studies have confirmed a strong association between the presence of a PFO and the risk for paradoxical embolism or stroke. In addition, there is significant evidence that patients with a PFO who have had a cerebral vascular event are at increased risk for future, recurrent cerebrovascular events. The presence of a PFO has also been linked to chronic migraine headaches. Although researchers are still investigating an explanation for the link, PFO closure has been shown to eliminate or significantly reduce migraine headaches in many patients
In certain cases, such as when anticoagulation is contraindicated, surgery may be necessary or desirable to close a PFO. The surgery would typically include suturing a PFO closed by attaching septum secundum to septum primum. This sutured attachment can be accomplished using either an interrupted or a continuous stitch and is a common way a surgeon shuts a PFO under direct visualization.
An atrial septal defect (ASD) is a defect in the septal wall of the heart between the heart's two upper chambers (the atria), and a ventricular septal defect (VSD) is a defect in the septal wall between the heart's two lower chambers (the ventricles). Septal defects of this type are sometimes referred to as a “hole” in the heart. Meanwhile, a patent ductus arteriosus (PDA) is a persistent opening between the aorta and the pulmonary artery. While this connection is normal for a fetus gestating in utero, if the opening fails to close soon after birth, the opening can allow blood to flow directly from the aorta into the pulmonary artery, which can put strain on the heart and increased the blood pressure in the lung arteries.
Umbrella devices and a variety of other similar mechanical closure devices have been developed for percutaneous closure of the defects described above. However, because of the unique geometries of each type of defect (e.g., PFO, ASD, VSD, or PDA), devices intended for one type of defect may not be optimally suited for use in another type of defect. Moreover, adapting a device developed for one type of defect to another type of defect may present certain challenges. Even if a device developed for a particular type of defect can be deployed within a defect of another type, some components of the device may insecurely seat against the septum and, thereby, risking thrombus formation due to hemodynamic disturbances.
In some cases, the size of the aperture is greater than the size of the center portion or other closure feature of the device. Upon deployment, such a device can slide toward one side within the aperture and thus occlude only one side or portion of the defect and result in a leak on the other side. Finally, some septal closure devices are complex to manufacture, which may result in inconsistent product performance.
The presently disclosed embodiments are designed to address these and other deficiencies of prior art septal closure devices.